Semiconductor device manufacturing: process – Packaging or treatment of packaged semiconductor – Assembly of plural semiconductive substrates each possessing...
Reexamination Certificate
1999-11-12
2002-07-30
Niebling, John F. (Department: 2812)
Semiconductor device manufacturing: process
Packaging or treatment of packaged semiconductor
Assembly of plural semiconductive substrates each possessing...
C438S124000, C438S126000, C438S127000, C438S637000
Reexamination Certificate
active
06426241
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a method for forming three-dimensional circuitization in a substrate and circuit formed and more particularly, relates to a method for forming conductive traces in a substrate for providing electrical communication between conductive regions by a molten solder screening technique and circuits formed by the technique.
BACKGROUND OF THE INVENTION
The circuitization process for electronic substrates usually involves several sequential processing steps. Among these steps are the initial chemical or physical machining of substrate line traces and via holes. Thereafter, the traces and holes are treated with various solutions to produce the metalized finish required to make them electrically conductive. A final step is then required to deposit joining metallurgy, usually of the solder type, to attach the electronic components. After surface grooves or via holes are first formed in the top surface or through a substrate and treated with a wetting material such as a flux, a suitable technique for filling the grooves and holes must be utilized to enable a reliable and low cost process for forming three-dimensional circuitization in the substrate. Suitable techniques that can be used for filling the grooves and holes can be selected from injection molded solder (IMS) technique or a molten solder screening (MSS) technique.
The IMS technique has been developed to replace a solder paste screening technique that is normally used in bumping semiconductor substrates. A major advantage of the IMS technique is that there is little volume change between the molten solder and the resulting solder bump. The IMS technique utilizes a head that fills boro-silicate glass molds that are wide enough to cover most single chip modules. A narrow wiper provided behind the solder slot passes the filled holes once to remove excess solder. The IMS method for solder bonding is then carried out by applying a molten solder to a substrate in a transfer process. When smaller substrates, i.e., chip scale or single chip modules (SCM's) are encountered, the transfer step is readily accomplished since the solder-filled mold and substrate are relatively small in area and thus can be easily aligned and joined in a number of configurations. For instance, the process of split-optic alignment is frequently used in joining chips to substrates. The same process may also be used to join a chip-scale IMS mold to a substrate (chip) which will be bumped.
A more recently developed method that alleviated the limitations of the solder paste screening technique of significant volume reductions between the initial paste and the final solder volume is the molten solder screening (MSS) method. In the MSS method, pure molten solder is dispensed. When the MSS solder-bumping method is used on large substrates such as 8 inch or 12 inch wafers, surface tension alone is insufficient to maintain intimate contact between a mold and a substrate. In order to facilitate the required abutting contact over large surface areas, a new method and apparatus for maintaining such are necessary.
For instance, in a co-pending application Ser. No. 09/070,121 commonly assigned to the Assignee of the present application which is hereby incorporated by reference in its entirety, a method for forming solder bumps by a MSS technique that does not have the drawbacks or shortcomings of the conventional solder bumping techniques has been proposed. In the method, a flexible die member is used in combination with a pressure means to enable the die member to intimately engage a mold surface and thus filling the mold cavities and forming the solder bumps. The flexible die head also serves the function of a wiper by using a trailing edge for removing excess molten solder from the surface of the mold.
The MSS process can be carried out by first filling a multiplicity of cavities in the surface of a mold with molten solder. This is accomplished by first providing a stream of molten solder and then passing a multiplicity of cavities in the mold surface in contact with the surface of the stream while adjusting a contact force such that the molten solder exerts a pressure against the surface of the mold to fill the cavities with solder and to remove excess solder from the surface of the mold. The stream of molten solder is supplied through a die head constructed of a flexible metal sheet that is capable of flexing at least 0.0015 inches per inch of the die length. The solder has a composition between about 58% tin/42% lead and about 68% tin/32% lead. The multiplicity of cavities each has a depth-to-width aspect ratio of between about 1:1 and about 1:10. The mold body is made of a material that has a coefficient of thermal expansion substantially similar to that of silicon or the final solder receiving material. The contact between the multiplicity of cavities and the surface of the molten solder stream can be adjusted by a pressure means exerted on the flexible die.
The MSS method is therefore a new technique for solder bumping large 8 inch or even 12 inch silicon wafers. As previously described, the technique basically involves filling cavities in wafer-sized mold plates with molten solder, solidifying the solder and then transferring the solder in these cavities to the wafer. The transfer process requires aligning the cavities in a mold plate to the solder receiving pads on a silicon wafer and then heating the assembly to a solder reflow temperature. This results in the molten solder to metallurgically bond to the metalized pads on the wafer and thus assuring the solder in each cavity to transfer from the mold plate to the wafer. Since various solder alloys are readily processed with the MSS technique, the mold plate and wafer assembly must remain aligned throughout the reflow process. Since the contact area between mold plate and wafer covers an entire 8 inch or 12 inch silicon wafer, it is important that these materials match very closely in coefficient of thermal expansion (CTE), for instance, when the mold plate is fabricated of a borosilicate glass.
It is therefore an object of the present invention to provide a method for forming conductive traces in a substrate that does not have the drawbacks or shortcomings of a conventional method.
It is another object of the present invention to provide a method for forming conductive traces in a substrate that does not require the wet-processing technique of electrodeposition.
It is a further object of the present invention to provide a method for forming conductive traces in a substrate that is capable of producing high quality circuits at low cost.
It is another further object of the present invention to provide a method for forming conductive traces in a substrate by scanning the substrate with an injection molded solder technique.
It is still another object of the present invention to provide a method for forming conductive traces in a substrate by utilizing the molten solder screening technique.
It is yet another object of the present invention for forming conductive traces in a flexible substrate such as a polyimide film for forming flexible circuits.
It is still another further object of the present invention to provide a method for forming conductive traces and vias in a plastic laminated board in a three-dimensional circuitization.
It is yet another further object of the present invention to provide an electronic substrate which includes a substrate of insulating material and at least one surface trace and via contact filled with a conductive metal for providing electrical communication between two conductive regions.
SUMMARY OF THE INVENTION
In accordance with the present invention, a method for forming conductive traces and via contacts in a substrate and circuits formed therefrom are provided.
In a preferred embodiment, a method for forming conductive traces in a substrate can be carried out by the operating steps of providing a substrate of a substantially electrically insulating material, forming grooves and apertures in a top surface of and thr
Cordes Steven A.
Ference Thomas G.
Gruber Peter A.
Howell Wayne J.
Speidell James L.
Jones Josetta I.
Trepp Robert M.
Tung Randy W.
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